This present invention relates generally to techniques for performing wellsite operations. More specifically, the present invention relates to techniques for sealing a wellhead of a wellbore.
Various oilfield operations may be performed to locate and gather valuable downhole fluids. Oil rigs are positioned at wellsites, and downhole tools, such as drilling tools, are deployed into the ground to reach subsurface reservoirs. Once the downhole tools form a wellbore (or borehole) to reach a desired reservoir, casings may be cemented into place within the wellbore, and the wellbore completed to initiate production of fluids from the reservoir. Tubulars (or tubular strings) may be provided for passing subsurface fluids to the surface.
A wellhead may be provided about a top of the wellbore for supporting casings and/or tubulars in the wellbore. A wellhead connector may be provided for connecting the wellhead to surface components, such as a blowout preventer (BOP) and/or a Christmas tree. Examples of wellhead connectors are described in U.S. Pat. Nos. 4,606,555 and 5,332,043.
Leakage of subsurface fluids may pose an environmental threat if released from the wellbore. A BOP may be positioned about the wellbore to form a seal about the tubular therein to prevent leakage of fluid as it is brought to the surface. Some BOPs may have selectively actuatable rams or ram bonnets, such as pipe or shear rams, for sealing and/or severing a tubular in a wellbore. Examples of BOPs and/or rams are provided in U.S. Pat. Nos. 7,367,396, 7,8149,79, and 2011/0000670. Some BOPs may be spherical (or rotating or rotary) BOPs as described, for example, in U.S. Pat. Nos. 5,588,491 and 5,662,171.